Radio scanning system



Patented Nov. 24, 1953 UNITED STATS PTENT OFFlCE RADIO SCANNING SYSTEMSecretary of the Navy Application July 22, 1950, Serial No. 175,404

6 Claims.

This invention relates to directional seaming antennas for use in radarsystems.

In some radar systems, the scanning antennas are required to searchrectangular areas. In the past this has been accomplished by starting atthe upper left-hand corner and sweeping horizontally across, and by thenstepping down and sweeping horizontally back, this being repeated untilthe entire area is swept. This method requires limit switches forreversing the horizontal and vertical drive motors.

According to this invention, a scanning antenna is moved vertically upand down periodically to substantially follow a sine wave or triangularwave of position as a function of time, while at the same time it ismoved horizontally back and forth periodically to substantially follow asine wave or triangular wave of position as a function of time, at ahigher or a lower frequency. This results in the scan beam tracing thepattern of a Lissajous figure while it sweeps a rectangular area at afaster rate than the prior parallel sweeps, and without the previouslyrequired limit switches. Another feature of this invention i that thescanning traces overlap over most of the area searched.

An object of this invention is to increase the rate of search of arectangular area by a scanning antenna.

Another object of the invention is to simplify scanning antennas usedfor searching rectangular areas.

Another object of the invention is to more thoroughly search arectangular area with a scanning antenna.

Another object of the invention is to search an area With a scanningbeam which forms a Lissajous figure.

The invention will now be described with reference to the drawing, ofwhich:

Figure 1 is a simplified diagrammatic view of one embodiment of thisinvention;

Fig. 2 is a graph illustrating the first half of a search patternprovided by the apparatus of Fig. 1, and

Fig. 3 is a graph illustrating the second half of the search pattern.

Referring now to Fig. 1 of the drawing, the constant speed, electricmotor l9 rotates the gear H of relatively large diameter which is meshedwith the gears 52 and :3 of relatively small diameter, the gear 53having, however, a larger diameter than the gear It.

The gear I2 has adjacent its perimeter, the pin M in the slot I 5 in thecrosshead 18.

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crosshead (6 has attached thereto the arm I! which is slidablehorizontally in the fixed support I8, and which has the gear teeth 59 onits upper surface. The teeth I 9 are meshed with the gear 20 whichdrives the elevation Selsyn generator 2|.

The generator 2| is connected through the control transformer 22 and theelevation control amplifier 23 to the elevation servo-motor 24 which isconnected through the elevation position generator 37 to the verticaldrive of the scanning antenna 25. Error voltages from the generator 31are fed back to the transformer 22 as is usual.

The gear l3 has adjacent its perimeter, the pin 26 in the slot 21 of thecrosshead 28. The crosshead 28 has attached thereto the arm 29 which isslidable horizontally in the fixed support 39, and which has the gearteeth 3! on its upper surface. The teeth 3t are meshed with the gear 32which drives the azimuth Selsyn generator 33.

Ihe generator 33 is connected through the azimuth control transformer315, azimuth control amplifier 35 to the azimuth servo-motor 3B which isconnected through the azimuth position generator 38 to the horizontaldrive of the antenna 25. Error voltages from the generator 38 are fedback in the usual manner to the transformer 34.

In operation, as the gears l2 and 13 are rotated by the gear II, themotions of the pins M and 26 in the slots of the crossheads l6 and 28respectively, cause the arms I! and 29 to reciprocate horizontally insine waves of acceleration as a function of time. This causes the gears20 and 32 of the generators 2i and 23 respectively, to rotate back andforth, and to deliver sine wave voltages to the control transformers 22and 34 respectively.

The voltage from the generator 2| is supplied through the transformer 22and the amplifier 23 to the servo-motor 24 Which moves the antennavertically up and down in a sine wave of acceleration as a function oftime, similar to that imparted to the generator 2 I.

The voltage from the generator 33 is supplied through the transformer 34and the amplifier 35 to the servo-motor 36 which moves the antenna backand forth horizontally in a sine wave of acceleration as a function oftime, similar to that imparted to the generator 33.

The ratio of the pitch diameters of the azimuth and elevation gears 83and i 2 should be the same as the scanning ratio, typically 10:9 or15:14, etc.

The ratio of the diameter of the azimuth gear by Fig. 2, followed by asweep such as that illus.--

trated by Fig. 3, after which the sweep of. Fig. 2 will be repeated,etc.

The unsearched area in. two of the corners. of Fig. 2 is seen to besearched by the sweep of Fig. 3, and the unsearched area in two of thecorners of Fig. 3 is seen to be searched by the following sweep of Fig.2.

This Lissajous type sweep covers the same area 7 in 11.5 seconds thatthe conventional parallel sweeps covers in 12.6 seconds.

Figs. 2 and 3 assume that the antenna has a 10 beam, and 10 between.half-power points. They also. assume a maximum allowance acceleration of425 per second squared, and a maximum allowable velocity of 150 persecond.

As illustrated by Figs. 2 and 3, the scanning spots. to overlap exceptat the very center of the area where they are tangent. With parallel andspiral searches the traces are tangent over the entirearea.

Square waves of acceleration as a function of time can be used insteadof the illustrated sine waves with. little effect on the form of thesweep illustrated by Figs. 2 and 3, and would result in about a 10%saving in time.

While the Lissajous type of search is particularly suited for scanningrectangular areas, its simplicity of generation shows it has advantagesover the conventional spiral search method as well as over theconventional parallel search method.

We claim as our invention:

1. An antenna system comprising a directional antenna, first motor meanshaving a rotor for cyclically moving said antenna alternatey in oppositedirections at one frequency, and second motor means having a rotor forcyclically moving said antenna alternately in opposite directionsdifferent from said first-mentioned directions,

and at a frequency different from said one. fre- 5 quency, and controlmeans for effecting the rotation of said rotors at respectivelypredetermined frequencies.

2. An antenna system comprising a directiona1 antenna, means including afirst motor having a rotor for cyclically moving said antenna verticallyup and down at one frequency, and means 4 including a second motorhaving a rotor for cyclically moving said antenna horizontally back andforth at a frequency different from said one frequency such that asubstantially Lissajous figure is formed.

3. An antenna system comprising a directional antenna, meansincludingan. elevation servomotor for moving said antenna vertically upand down, means including an azimuth servo-motor for moving said antennahorizontally back and forth, an elevation Selsyn generator having arotor and connected to said elevation servornotor, an azimuthv Selsyngenerator having a rotor and connected to said azimuth servo-motor, andmeans for cyclically rotating the rotors of said generators in oppositedirections at different frequencies.

4. An antenna system comprising a directional antenna, means includingan elevation motor having a rotor for moving said antenna vertically upand down, means including an azimuth motor having a rotor for movingsaid antenna horizontally back and forth, and means for cyclicallyrotating the rotors of said motors in opposite directions at differentfrequencies.

5. An antenna system comprising a directional antenna, means including afirst motor having a rotor and adapted for moving said antenna inopposite directions, means including a second motor having a rotor andadapted for moving said antenna in opposite directions different fromsaid first-mentioned directions, and means. for cyclically rotating therotors of said motors. in opposite directions at diiferent frequencies.

6. An antenna system comprising a directional antenna, means including afirst servo-motor for moving said antenna in opposite directions, meansincluding a second servo-motor for moving said antenna in oppositedirections diiferent. from said first-mentioned directions, av firstSelsyn generator having a rotor and being connected to said firstservo-motor, a second Selsyn generator having a rotor and connected tosaid second servomotor, and means for cyclically rotating the rotors ofsaid generators in opposite directions at different frequencies.

GORDON LEY. CHARLES H. JONES.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 2,231,929 Lyman Feb. 18, 1941 2,410,666 Leck Nov. 5, 19462,410,831 Maybarduk et a1. Nov. 12, 1946 2,526,314 Alexanderson et a1.Oct. 17, 1950

